Add ESLint, Prettier, and pre-commit hook

eslint.config.js

@@ -0,0 +1,30 @@
+import js from "@eslint/js";
+import ts from "typescript-eslint";
+import reactHooks from "eslint-plugin-react-hooks";
+import reactRefresh from "eslint-plugin-react-refresh";
+import prettierConfig from "eslint-config-prettier";
+
+export default ts.config(
+  { ignores: ["**/dist/**", "**/node_modules/**", "backend/**"] },
+  {
+    extends: [js.configs.recommended, ...ts.configs.recommended],
+    files: ["frontend/src/**/*.{ts,tsx}"],
+    plugins: {
+      "react-hooks": reactHooks,
+      "react-refresh": reactRefresh,
+    },
+    rules: {
+      ...reactHooks.configs.recommended.rules,
+      "react-refresh/only-export-components": ["warn", { allowConstantExport: true }],
+      // TypeScript handles unused-vars via tsconfig strict flags
+      "@typescript-eslint/no-unused-vars": "off",
+      // Allow explicit any in a few cases (PixiJS / AlphaTab interop)
+      "@typescript-eslint/no-explicit-any": "warn",
+      // Empty catch blocks are intentional in WebMidi / PixiJS teardown paths
+      "no-empty": ["error", { allowEmptyCatch: true }],
+      // Control-character regexes are intentional input sanitization
+      "no-control-regex": "off",
+    },
+  },
+  prettierConfig
+);